Geothermal

Geothermal energy uses the heat of the earth to provide direct heat or electricity production. Direct heat geothermal uses low to moderate temperature water to heat structures, grow plants in greenhouses, and in industrial processes such as drying food or fish farming. These systems pump hot water directly into the structures they are warming. Producing electricity from geothermal uses high temperature resources to convert heat into power, though new technologies are emerging that allow lower temperature resources to be utilized in electricity generation.

Currently, three types of geothermal electric generators are in use:

Dry stream power plants use steam emitted directly from geysers or fumaroles to turn turbines and create electricity. These require relatively rare, very hot hydrothermal systems, where almost all the water is in steam form under the surface of the earth. The United States’ largest producer of geothermal energy, The Geysers in northern California, is an example of dry stream power plants. The Geysers have a combined 1,517 MW of installed capacity, with a 63% capacity factor.

Flash steam power plants require geothermal fluids in excess of 360°F. These fluids are pumped into a tank held at a very low pressure, causing the fluids to vaporize instantly. The resulting steam is used to drive a generator. Most geothermal power plants in operation today are flash steam power plants.

Binary-cycle power plants use a new technology that requires only moderately hot water. These power plants generate electricity by pumping hot water into a heat exchanger where a fluid with a lower boiling point than water is stored. The hot water causes the other fluid to vaporize and the resulting steam turns a turbine to generate electricity. The fluid is cooled and returned to the heat exchanger, creating a closed system. Many flash steam power plants also employ a binary cycle to capture more energy after the very hot geothermal fluids have condensed and cooled. Since most geothermal resources in the world are low-to-moderate heat, the number of binary-cycle power plants in operation will likely increase in the future.

Geothermal Potential in Alaska

Alaska’s location on the Ring of Fire, a volcanic arc circling the Pacific Ocean, means there are many opportunities for geothermal development in the state. There are over 130 volcanoes and volcanic fields that have been active in Alaska in the last two million years, and more than 50 that have been active within historical time (since 1786). Additionally, 100+ sites with thermal springs and wells have been identified across the state. In a project completed in 1982, the USGS identified four major regions that warranted further study for their geothermal potential. These regions were 1) the Interior Hot Springs, running east-west from Canada’s Yukon Territory to the Seward Peninsula, 2) the Southeast Hot Springs north-east of Ketchikan, 3) the Wrangell Mountains and 4) the Ring of Fire volcanoes on the Aleutian Chain, the Alaska Peninsula, and Mt. Edgecumbe on Kruzof Island. The Interior and Southeast both have low to moderate geothermal systems with surface expression as hot springs. The Wrangell Mountains have several active volcanoes with unknown geothermal energy potential. The Ring of Fire hosts several high-temperature hydrothermal systems, typically seen on the surface as host springs, geysers and fumarole fields.

While some communities in Alaska are considering using geothermal resources for energy production, the greater value to Alaskans from geothermal sources may be direct heat. An Institute of Social and Economic Research (ISER) study showed that the average annual cost for heating a home in Alaska was around $4500 at May 2008 prices. Geothermal direct heat could provide an environmentally sound way to effectively heat many homes in Alaska at a reduced price. While new technologies are making energy production from geothermal sources more economically viable, the greatest challenge to Alaskans is the remote location of much of our geothermal potential.

Chena Hot Springs. Photo courtesy of Chena Hot Springs Resort.

In the Interior, Chena Hot Springs Resort is an example of diverse geothermal energy use – providing heat and power to its facilities, swimming pools and greenhouses. The resort utilizes organic rankine cycle generators with a total capacity of 680 kW that run on 165°F water, the lowest temperature for an operating geothermal power plant in the world. The original $2.1 million project displaces 160,700 gallons of diesel annually and is projected to save over $500,000. The site also demonstrates the use of geothermal energy for refrigeration. The resort installed a 16-ton absorption chiller in 2005 to cool an outdoor ice museum year-round. The chiller uses water from a 165°F well as a heat source, and a 40°F creek as a heat sink. This technology has potential applications in other Alaska communities that could use waste or geothermal heat to provide cooling for fish processing, ice production and community cold storage. Research is ongoing at Chena Hot Springs to determine the full geothermal potential of the area, with the goal of fully powering the resort with clean geothermal power and providing a blueprint for geothermal development projects in other parts of Alaska.

Exploration of geothermal potential is increasing statewide. Ongoing studies are underway 80 miles west of Anchorage at Mt. Spurr. In 2008 the State awarded geothermal leases to Ormat Technologies, Inc. After extensive investigations and drilling in 2011, Ormat did not encounter temperatures capable of supporting a power plant. The company is now looking for other drilling targets within the lease area. Akutan in the Aleutians is another potential geothermal site. In 2010, the City of Akutan drilled two exploratory wells at Hot Springs Valley, encountering 359° F water at 585 feet. Exploratory fieldwork continued through 2012 in preparation for additional drilling.

Exploration in the 1980s near Mt. Makushi outside of Dutch Harbor indicated that tens of megawatts could be generated from geothermal resources there. In 2012, several exploration wells were completed at Pilgrim Hot Springs on the Seward Peninsula in order to assess the region’s resource potential. A 2011 reconnaissance study has also been examining a potential geothermal resource at Tenakee Inlet Hot Springs in Southeast Alaska.

Ground source heat pump (GSHP) systems are another use of geothermal energy. The electrically powered systems tap the relatively constant temperature of surrounding earth or water bodies to provide heating and cooling. More than 50,000 of these systems are installed in the US each year. In Alaska, heat pump systems are used for space heating homes commercial buildings and public facilities. The Juneau Airport GSHP, in operation since 2011, has saved an estimated $190,000 in displaced diesel fuel. GSHP systems are most applicable in areas with low electric rates and high heating costs. Geotechnical conditions like permafrost are also a factor.